Concrete serves as the primary material for foundations and roadways. Unfortunately, concrete possesses several inherent drawbacks. First, concrete shrinks when it hardens which often results in cracking. Cracks may be controlled by placing joints (pre-planned cracks) in the concrete slab. Further cracks may develop over the life of the slab due to concrete's low tensile strength, shrinkage, and thermal expansions and contractions.
Joints and cracks in concrete are normally the weakest part of a concrete slab. A non-reinforced joint or crack cannot transfer loads from one slab to the next. Concrete pavements with poor load transfer often suffer from faulting at the joint. Joint faulting is a well known type of premature fatigue failure caused by the passage of traffic over transverse joints in concrete roads without sufficient load transfer. Advanced stages of faulting can lead to further cracking, crumbling, and damage of the concrete slab.
Modern pavements reduce the possibility of faulting by improving the sub-base support, including dowels to transfer loads between the slabs at the joints, and sealing the joints. Properly designed joints, along with regular maintenance programs, have made possible the construction of durable, high-quality concrete pavements that will perform well for many years.
Unfortunately, many roads designed in the past and currently used do not contain adequate design features. Many roads did not use dowels. For some of the roads with dowels, the dowels have failed. Other roads have cracked under severe or unpredicted use. Many of these roads have developed faulting problems.
Faulting was originally cosmetically repaired with asphalt overlays and diamond grinding. These methods covered up or removed the fault differential, but they did not address the poor load transfers at the joints and cracks. As a result, faulting often reoccurred.
Newer concrete pavement restoration techniques attempt to address the problem of poor load transfer. Highway agencies have tried to retrofit dowels, double-V shear devices, figure-eight devices, and miniature I-beam devices to restore load transfer with some success. The problems with these techniques lie within the implanted devices and the material holding the devices in place. In these techniques, the implanted device transfers the vast majority load across the joint. These devices may fail if they are subject to unpredicted loads or are improperly placed in the encasing medium. Often it is difficult to ensure that the implanted device is properly positioned. Furthermore, many of these devices are made of material which could corrode and fail or, even worse, pose a safety hazard should one come loose. Finally, load transfer devices sometimes do not effectively bond with the material encasing it. Without bonding, the surrounding material cannot help to bear the load across the joint.
The second problem with current load transfer restoration techniques is with the material used to encase the load bearing device. The materials used often cannot effectively bear tensile loads and/or are difficult to handle in the field. Material used to encase load transfer devices include cementitious grout and polymer concretes containing polyesters, epoxy or methacrylate. These materials are designed to match the thermal expansion modulus of concrete, but cannot bear sufficient tensile loads or are not flexible enough to distribute loads throughout the material. Furthermore, these materials are too viscous to flow into narrow slots and cracks in concrete. The primary function of the filler materials is to bond the load-carrying device to the adjacent slabs and to keep the load-carrying device in place. Nothing suggests using filler material to transfer loads across concrete joints. What is needed is an improved method of restoring or improving load transfer across joints in concrete pavement.